The present invention relates to the corrections of distortions in PCM signals, particulary those stored on digital audio record discs.
PCM transmission devices generally assure a high transmission quality and offer the possibility for substantially reconstititing the original values of incorrect, or disturbed, samples. However, pure data transmission requires a very low residual error probability, whereas for PCM audio transmission devices it is sufficient to reduce residual errors only to a degree which is no longer audible on the playback side.
Interlacing methods, parity checks and redundancy increasing codes are used to secure the data on a PCM transmission path. Residual errors which remain in spite of all these measures can be attenuated by interpolation between undisturbed sample values to the extent that these errors can no longer be noticed in a playback device.
The technical information accompanying the PCM 1 Audio Unit manufactured by Sony (1978) discloses an average value interpolation in which an error word is replaced by the average value of the preceding and of the next following word. The error is thus compensated in such a manner that no audible difference results. The compensation capability realizable with this process is an advance over the process in which the preceding data word is used as a replacement for the disturbed data word.
Elektronics Weekly, Dec. 29, 1976/Jan. 5, 1977, also discloses a method for interpolation of disturbed sample values in which an interpolation is performed between two points between which a disturbed sample occurs.
The known methods fail if an interpolation is to be made between sample values between which there is more than one disturbed sample value. Two or more successive disturbed sample values then result in a noticeable error at the playback end.